It all started going to the dogs when the multinationals decided to consolidate their brands, so Marathon bars in the UK became Snickers (the US name), and Jiff cleaner became Ciff (why would you want to clean your kitchen with a thick, yellow liquid that sounds like it was named after a venereal disease?(for those outside the UK, the C is pronounced as an S))

Nestle definitely used to be pronounced 'Nessles' to rhyme with wrestles
Original milky bar ad
Listen carefully at the very end.
Interestingly, on the 30th anniversary ad they dubbed the original soundtrack with the French pronunciation. Bastards.

Nestlé originated in a 1905 merger of the Anglo-Swiss Milk Company, which was established in 1866 by brothers George Page and Charles Page, and the Farine Lactée Henri Nestlé Company, which was founded in 1866 by Henri Nestlé.

So it would have been "Ness-Lay" without any doubt. Of course, by the time they started selling in English markets, they'd probably call themselves "Nessles". But I bet they died a little. But not as much as all the poisoned African babies, of course.